1. Field of the Invention
The present invention relates to an electric power converter for a vehicle connected between an alternating-current generator and a direct-current device.
2. Description of the Background Art
An electric power converter for a vehicle which performs electric power conversion between a direct-current device, such as a battery or a lighting device, and a generator which is an alternating-current device is used for a vehicle, such as an automobile mounted with an alternating-current generator for a vehicle (hereinafter referred to as a generator).
Generally, such an electric power converter for a vehicle is connected between a generator and a battery, and a multi-phase bridge circuit is constituted by a plurality of diode elements. The electric power converter for a vehicle rectifies the alternating-current power generated by the generator by means of the aforementioned multi-phase bridge circuit, converts the alternating-current power into direct-current power, and supplies the direct-current power to the battery.
In recent years, an electric power converter for a vehicle using a switching element and a parasitic diode annexed thereto, and using rectification (hereinafter referred to as synchronous rectification) by the switching element has been proposed instead of the diode since the rectification using the switching element is more efficient than the rectification using the diode bridge, and is of less generation of heat of the elements. The proposed electric power converter for a vehicle has been adapted so that an execution permission signal (hereinafter referred to as a diode ON signal) of synchronous rectification is generated depending on the energization state of a parasitic diode, and switching control of the switching element is performed on the basis of this diode ON signal (described in, for example, JP-A-2009-284564).
In the conventional electric power converter for a vehicle, a diode ON signal is generated from the energization state of a diode and a switching timing signal is generated on the basis of this diode ON signal, to perform switching control of the switching element. At this time, as a method of generating the switching timing signal from the diode ON signal, JP-A-2009-284564 suggests using a control allowance time in which the delay time of control and the rotational fluctuation of the generator are taken into consideration.
However, since a technique for optimizing this control allowance time is not suggested, there is a problem in that excess and deficiency of the control allowance time occur due to the rotational fluctuation or load fluctuation depending on setting methods of the control allowance time, and as a result, decreases in efficiency or switching mistakes occur.